The present invention relates to a microchannel array structure embedded in a silicon substrate and a fabrication method thereof; and, more particularly, to a structure of high-density ultra fine microchannel array buried deep in a silicon substrate by silicon surface micromachining using semiconductor batch processing.
Contrived for the development of physical and chemical micro sensors and mechanical driving elements such as micro actuators, the MEMS technology is expanding its applicable range day by day up to RLC passive components, RF and microwave devices, flat panel displays and core optical components for telecommunication, as highly integrated semiconductor technology deploys. These days, researchers vigorously get down on a study of fluidic MEMS technologies that can miniaturize conventional analyzers and improve their performance using microfluidics for DNA sequencing, research of protein functions, measuring of a very small amount of metabolic substances or reagents, especially in the areas of bio-engineering, genetic engineering, clinical diagnostics and the development of new medicines. Among the fluidic MEMS technologies is a lab-on-a-chip, which is being developed as a microfluidic platform for systemizing and integrating bio-chips such as DNA chips, protein chips, immuno-assays and the like. These devices are formed based on a plurality of microchannel structures such as microfluidic networks, as they conduct functions of separation, extraction, filtration, mixing and transport of reagents, liquids, or minute particles, making use of the principle of electrophoresis or dielectrophoresis with the aid of microcelectrodes. In the meantime, additional high-performance micro heaters are required for the embodiment of micro PCR (polymerase chain reaction) amplifiers, micro reactors and so forth. Microchannel structures are used to interconnect microfluidic components, e.g., micro pumps, micro valves, micro sensors in micro total analysis systems, drug delivery systems, HPLC (high performance liquid chromatography), etc., or used as separation columns as well as heat sinks and heat exchangers that cool down electronic components such as CPUs, infrared sensors, high power semiconductor lasers.
Microchannels with as many uses as mentioned above are usually fabricated by bulk micromachining, polymer-based micromachining, or surface micromachining. The bulk micromachining method mainly focuses on bonding and wet etching of a substrate itself, while surface micromachining features a technique of deposition or dry etching of thin layers on the top of a substrate.
For instance, microchannels are fabricated by locally processing a silicon, glass or quartz substrate with an etching solution, dry etching, or laser cutting, forming channel patterns, and is hermetically sealed by attaching another substrate thereto by anodic or fusion bonding, diffusion bonding or soldering. Another method of making microchannels are to form channel patterns by coating a thick polymer layer on the top of a substrate; radiating it with UV light; attaching another substrate to the top of the channels, or coating a polymer layer again on the formed channel patterns; then doing patterning of etch holes; and then removing the sacrificial polymer layer below the final polymer layer. Also, a microchannel can be fabricated by using a sacrificial oxide or photoresist layer. The sacrificial layer is filled up in the region where channels will be formed. A microchannel outer wall is deposited or electroplated on the top of the sacrificial layer, and then the sacrificial layer is removed by an etching solution. It""s also possible to make microchannels by patterning a thin masking film in slot shapes on the top of a substrate, anisotropically etching the substrate with an etching solution, thus forming channel patterns. Then, a thin layer is deposited on the entrances to hermetically seal up the channels.
As another substrate is to be attached to a thick polymer film or to a substrate where channel patterns are etched, the conventional methods seen above have problems of generating pores on the interface, so they are not appropriate to be applied to the fabrication of ultra fine microchannels whose width is less than tens of xcexcm, because it""s hard to control the channel size. Using two substrates, the manufacturing process is complex with narrow choice in selecting channel materials. Also, it""s hard to form such additional structures as micro sensors, micro actuators, passive elements and electronic devices on the top of a substrate. In case when a sacrificial layer is deposited or coated on a silicon substrate, the channel has a limitation on its height, thereby affecting the following step of photolithography, because it""s difficult to deposit the sacrificial layer thick more than a few xcexcm in CMOS semiconductor processes. The problem of the conventional method in forming channels inside a substrate is that the channel shape depends on the etching rate of the substrate you choose, and the width of channels is relatively as big as tens of xcexcm.
Putting an importance on the fabrication of a single or a few microchannels, the above methods have never been applied to the fabrication of ultra fine microchannels or microchannel arrays by using semiconductor processes and the integration of additional device structures thereby.
It is, therefore, an object of the present invention to provide a high-density ultra fine microchannel array structure embedded in a silicon substrate with a channel whose size is as fine as less than tens of xcexcm, preferably less than a few xcexcm, and a fabrication method thereof.
It is another object of the present invention to provide a microchannel array structure embedded in a silicon substrate, which can be fabricated by simple, semiconductor batch processing with a wide choice of selecting channel materials as well as the capability of forming additional structures such as micro sensors, micro actuators, passive components, electronic devices on the top of microchannels just by integrated semiconductor fabrication processing, and a fabrication method thereof.
It is further another object of the present invention to provide a microchannel array structure embedded in a silicon substrate with deep channel depth, minimizing the step height of the upper part of channel patterns so that the micro channel array structure can hardly affect later fabrication procedures.
To achieve the purposes above, the present invention provides a high-density ultra fine microchannel array structure with a planar surface embedded in a silicon substrate by surface micromachining using semiconductor batch processing, and a method of integrating a high-performance micro heater or a micro electrode integrated on the top of the microchannel array structure.
In accordance with the present invention, there is provided a method of fabricating a microchannel array structure, further including the steps of: a) forming a micro heater or a micro electrode by locally doping impurities into the top surface of the microchannel outer wall, or by depositing and etching an additional thin layer on the outer wall after the microchannel outer wall is formed; and b) forming electrical pads by depositing and etching a metal layer on the micro heater or the micro electrode.
In accordance with the present invention, there is provided a microchannel array formed with a plurality of microchannels, of which the planar structure shapes like a slot or an isolated column, and cross-sections of which shape like squares, rounds, hemicycles, lozenges, trapezoids, triangles, hexagon and so forth.
In accordance with the present invention, there is provided a microchannel array formed with highly integrated ultra fine microchannels whose sectional width, or diameter, is 10xe2x88x921xcx9c100 xcexcm long.
In accordance with the present invention, there is provided a microchannel array region has a sectional width, or diameter, of 100xcx9c103 xcexcm.
In accordance with the present invention, there is provided a microchannel outer wall formed out of polysilicon, amorphous or single-crystal silicon, conductors, insulators, or semiconductors.
In accordance with the present invention, there is provided a micro heater formed out of polysilicon, amorphous or single-crystal silicon layers, conducting layers, or semiconductor layers, otherwise, there is provided a micro electrode formed out of polysilicons, amorphous or single-crystal silicon layers, conducting layers, or semiconductor layers.